Concrete forms are used in the process of pouring the foundations of buildings under construction. These concrete forms, typically made of aluminum, are placed into position where the foundation walls will ultimately reside. Concrete is then poured into the forms and allowed to harden, after which the forms can be removed and later re-used. These concrete forms, despite being made of aluminum, typically weigh about 100 pounds and are difficult to handle because of their weight. The handling of concrete forms, therefore, has required heavy machinery in order to load and unload the forms at the construction site as well as to transport them to and from the site.
Traditionally, cranes have been used to lift and place the concrete forms. Before lifting, the forms were loaded several at a time into hoisting cages. This practice kept the forms from falling over, as they are not suited for standing on their own, and it also saved time and effort since several forms could be moved in a single lifting operation. When a foundation needed to be installed, a crane lifted the hoisting cages loaded with concrete forms from a truck into the hole dug for the foundation. The individual forms were then manually removed from the cage and put into place. After the cement cured, and the forms were no longer needed, they were loaded back into the hoisting cages and lifted back onto a truck. The truck transported the loaded hoisting cages to and from the building sites.
Concrete forms are relatively tall, so the cages used to hoist them were made taller still in order to accommodate them. This, however, presented serious problems during transportation of the cages. The trucks transporting the hoisting cages needed to be able to travel just about anywhere to get to and from the building sites, and this meant that they would have to go under obstacles such as highway overpasses. The standard lowest clearance for highway overpasses in the United States is 13 feet 6 inches, and this was too low for ordinary trucks loaded with hoisting cages to pass under. In an attempt to overcome this problem, special measures were taken to reduce the overall height of trucks loaded with hoisting cages. One such special measure was to modify the trucks, at added expense, in order to lower the height of the beds of the trucks, hence, lowering the overall height of the trucks when loaded with hoisting cages. This situation was undesirable since the transportation of hoisting cages became dependent on these specially modified trucks.
Prior hoisting cages were made of an assembly of steel bars welded together, resulting in cages whose total height was excessive. Typically, four vertical bars formed the edges of the cage and several horizontal bars spaced along the sides of the cage were welded to the vertical bars. Exterior inverted V-shaped trusses were welded to the top of the cage such that the bottom ends of the trusses were attached to the tops of the vertical bars. The apex of the trusses pointed directly upward, towering above the rest of the hoisting cage and forming the highest point of the cage. The truss is the part of the cage that is actually caught by the hoisting crane. The trusses therefore added unwanted height to the hoisting cage. A catch was attached to the trusses and provided a place for a lifting means to grasp the cage, specifically at the apex of the catch. The catch and the trusses provided a means for distributing the stress of the lifting operation to vertical bars within the cage. This stress distribution is important and if not done properly could easily deform the cage or worse yet, cause it to fail structurally. For instance, if the cage were lifted by a horizontal bar, this bar would flex and possibly become permanently bent or even snap. Therefore, the truss is an important structural element in the hoisting cage. However, the additional height of the cage due to the truss being positioned at the top of the cage made the problem of transporting the cage much worse than it needed to be.
Therefore, it is a primary object of the present invention to provide a hoisting cage that is not significantly taller than the concrete forms it is designed to hoist and, therefore, allow the cage to be transported along standard United States highways and roads without the need for modifying the transporting trucks.
It is another object of the present invention to provide a hoisting cage with an interior truss built into the sides of the cage which can withstand the stresses due to lifting the cage and to transmit and distribute those stresses to vertical members of the cage.
It is a further object of the present invention to provide a hoisting cage with a catch for connecting the apex of the interior truss to a lifting apparatus. The catch can fold out of the way in order to reduce the overall height of the cage during transportation.
It is yet a further object of the present invention to provide a hoisting cage whose trusses can fold up in order to connect to a lifting means and also fold down to reduce the overall height of the cage during transportation.